Centering catheter with improved perfusion

ABSTRACT

A centering catheter with engagement knobs to provide improved perfusion in a vessel during intravascular radiation therapy. In one embodiment, a helical centering balloon catheter includes a helical centering balloon formed of helical lobes having a plurality of engagement knobs that outwardly protrude from the helical lobes. The helical lobes form a main spiral perfusion channel for perfusion of blood past the centering catheter. The engagement knobs compliantly engage the vessel walls and offset of the helical lobes such that auxiliary perfusion channels are formed around the engagement knobs between the helical lobes and the walls of the vessel to allow additional perfusion. In the event of a partial obstruction of the spiral channel or a single point failure, the auxiliary perfusion channels allow perfusion past the obstruction.

FIELD OF THE INVENTION

The present invention relates to the field of intravascular radiationtherapy. In particular, the present invention relates to catheters usedfor intravascular delivery of radiation.

DESCRIPTION OF RELATED ART

Coronary artery balloon angioplasty is a minimally invasive techniquedeveloped as an alternative to coronary artery bypass grafting fortreatment of atherosclerosis, the principle process of heart disease.There are about 450,000 coronary interventions, i.e., angioplasty,atherectomy, and stent, performed annually in the U.S. However, a majorlimitation of this clinical procedure is the high prevalence ofrestenosis, or re-narrowing, of the treated vessel. Restenosis occursapproximately 30-50% of the time.

Restenosis occurs as result of injury to the vessel wall due to theangioplasty procedure, or to other procedures, i.e., stenting,atherectomy, that compress or remove the atherosclerotic material andmay cause trauma to the vessel. Restenosis is a complex process, whichcan involve an immediate vascular recoil, neointimal hyperplasia, and/orlate vascular remodeling. Neointimal hyperplasia, a response of the bodyto balloon-induced physical injury of the vessel wall, is thought to bethe main contributor to restenosis. Hyperplasia can result in narrowingof the vessel lumen within 3-6 months after angioplasty due toproliferation of smooth muscle cells in the region traumatized by theangioplasty. Restenosis can require the patient to undergo repeatangioplasty procedures or by-pass surgery with added costs and risks tothe patient.

One method currently used to inhibit restenosis following a proceduresuch as angioplasty, involves delivery of a prescribed dose of radiationto the walls of the dilated length of vessel through intravascularradiotherapy (IRT). In an example of one method of IRT, a catheter isinserted into a vessel and positioned within the length of vesseldilated by the angioplasty procedure. Once the catheter is positioned, aradiation source is inserted into the lumen of the catheter andpositioned to allow delivery of a prescribed dose of radiation to thevessel over a period of time. As a radiation source is relatively small,the radiation therapy may require the radiation source to remainpositioned a minimum of four minutes in the vessel. To maintain theposition of the catheter within the vessel, some IRT catheters arestructured to engage the vessel walls until the radiation therapy iscomplete.

A consideration in the design of the above IRT catheters is the effecton blood flow in the vessel. If an IRT catheter is structured so that itobstructs blood flow within the vessel over a prolonged period, forexample, more than one minute, this may result in impaired heartfunction, angina, cardiac arrest, or myocardial infarction. Should a lowblood flow rate, e.g., a low perfusion flow rate, be detected, the IRTis typically stopped and the catheter withdrawn to allow the blood flowto reestablish and the area to recover. The IRT must then be restartedto complete the therapy session. This can result in a prolongedtreatment period and discomfort to the patient.

Alternatively, if an IRT catheter is structured much smaller than thevessel diameter to allow a higher perfusion flow rate, the catheter maynot adequately engage the vessel wall and the radiation source may notbe centered such that the vessel would receive a non-uniform delivery ofthe radiation.

For a given radiation source, the intensity of the radiation dropsrapidly as a function of distance from the source axis, i.e., a smallchange in distance from the source to the surface of the vessel wall canresult in a large difference in the radiation intensity. Thus, if theradiation source is positioned close to the vessel wall, the wall mayreceive an overdose of radiation, e.g., a “hot” spot develops.Overdosing a vessel wall with radiation can result in vessel damage,such as inflammation, hemorrhaging, and arterial necrosis. Conversely,the opposite side of the vessel may receive an underdose of radiationthat may result in no inhibition of restenosis.

In order to mitigate both the effects of low perfusion flow rates and ofoverdosing or underdosing a vessel, other catheters, such as centeringcatheters have developed structures which compliantly engage, orself-fit within, the walls of the vessel to both deliver anapproximately uniform dose of radiation and to maintain the catheterposition within the vessel. Typically, portions of the catheterstructure contact the vessel wall while providing openings for perfusionpast the catheter.

U.S. Pat. No. 5,643,171 to Bradshaw et al. describes several embodimentsof a centering catheter that may be used with IRT. In one embodiment, acentering balloon is attached to the portion of the catheter in whichthe radiation source is to be located. The centering balloon can then beinflated until it compliantly engages the vessel wall. In oneembodiment, the centering balloon may be formed of helical lobes thatsubstantially center the radiation source within the lumen of the vesseland allow perfusion past the catheter through a main spiral perfusionchannel created between the helical lobes of the balloon.

However, it has been noted that single point failures can occur duringuse of the helical balloon structure, as well as in other structureswith a continuous perfusion channel, such as spiral structures. Singlepoint failures occur when an obstruction, such as plaque debris or ablood clot, block perfusion through the main spiral perfusion channel.As the helical structure uses compliant engagement to maintainpositioning, portions of the catheter contact the vessel wall andprevent perfusion past the blockage through an alternate path. Thus, theobstruction can cause the perfusion flow rate, even with the helicalcentering catheter, to stop or to drop to such a low rate that the IRTmust be discontinued until the area is recovered.

Thus, what is needed is an apparatus for improving perfusion incentering catheters with helical or spiral shaped base forms in order tomitigate the effects of single point failures.

SUMMARY OF THE INVENTION

The present invention includes a centering catheter for improvedperfusion which has a centering segment with lobes which form at leastone main perfusion channel, and a plurality of engagement knobs thatcompliantly engage the walls of the vessel and form auxiliary perfusionchannels.

DESCRIPTION OF THE DRAWINGS

The present invention may best be understood by referring to thefollowing description and accompanying drawings which are used toillustrate embodiments of the invention. In the drawings:

FIG. 1 illustrates one embodiment of the present invention positionedwithin a vessel.

FIG. 2 illustrates a longitudinal cross-sectional view of the embodimentof the present invention shown in FIG. 1.

FIG. 3A illustrates a transverse sectional view of the embodiment of thepresent invention shown in FIG. 1 taken along line 3—3.

FIG. 3B illustrates a transverse sectional view of the embodiment of thepresent invention shown in FIG. 3A with a blockage of the main perfusionchannel.

FIG. 4 illustrates another embodiment of the present invention.

FIG. 5 illustrates a transverse sectional view of the embodiment of thepresent invention shown in FIG. 4 taken along the line 5—5.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes a centering catheter with engagementknobs to provide improved perfusion in a vessel during intravascularradiation therapy.

FIG. 1 illustrates one embodiment of the present invention positionedwithin a vessel. The embodiment of FIG. 1 includes a helical ballooncentering catheter 10 which has a cylindrical shaft 12 having a proximalend and a distal tip 14 and a helical centering balloon 16 locatedproximal to the distal tip 14. It is to be understood that although thepresent example is discussed with reference to a helical structurecentering catheter, the present invention may be used to improveperfusion of other catheters that utilize compliant engagement within avessel, for example, straight channeled catheters. In the illustration,the helical balloon centering catheter 10 is shown positioned within alength of vessel 32 that is to receive intravascular radiation therapy(IRT). In one example, the helical centering balloon 16 may bepositioned within a length of vessel 32 that has been dilated using anangioplasty procedure and is to receive a prescribed dose of radiationto prevent restenosis of the dilated length.

In one embodiment, the helical centering balloon 16 may be formed as acontinuous, inflatable, spiral of helical lobes 26 with a plurality ofengagement knobs 30 that externally protrude from the helical lobes 26.In one embodiment, the engagement knobs 30 are formed as an integralpart of the balloon lobe shape of the helical lobes 26. As the helicallobes 26 advance and spiral along the length of the helical centeringballoon 16, a continuous main spiral perfusion channel 28 is formedbetween the helical lobes 26 that allow perfusion past the catheter 10.The engagement knobs 30 act to compliantly engage the walls of thevessel 32 when the helical centering balloon 16 is inflated, andmaintain the position of the helical balloon centering catheter 10within the vessel 32 during radiation therapy. Additionally, theengagement knobs 30 offset the helical lobes 26 a small distance awayfrom the wall of the vessel 32 to create auxiliary perfusion channels 34for increased perfusion past the helical balloon centering catheter 10.In the event that the main spiral perfusion channel 28 becomes partiallyobstructed or experiences a single point failure, the auxiliaryperfusion channels 34 provide alternate paths for perfusion past theobstruction. It is to be noted that in compliantly engaging the vesselwalls, the engagement knobs 30 may flatten somewhat, thus the perfusionflow rate through the auxiliary perfusion channels 34 may vary dependingupon the fit of the helical centering balloon 16 within the vessel 32.In the present example, the engagement knobs 30 may be formed as hollow,teardrop-shaped outward protrusions of the helical lobes 26. In anotherexample, described further herein with reference to FIGS. 4 and 5, theengagement knobs 30 may also be hemispherical in shape. Other shapes mayalso be utilized so long as the shape allows for compliant engagement ofthe vessel wall and formation of auxiliary perfusion channels.

In one embodiment, the engagement knobs 30 may be located along theouter spiral midline of the helical lobes 26 with a spacing of five (5)engagement knobs 30 per revolution. Other numbers of engagement knobs 30and spacing per revolution may also be used, but a spacing of three tofive (3-5) engagement knobs 30 per revolution is preferred. Further, theengagement knobs 30 may be positioned in patterns, other than along thespiral midline, for example, in a random pattern, or in multiple rows.

FIG. 2 illustrates a longitudinal cross-sectional view of the exampleshown in FIG. 1. The shaft 12 has a lumen 18 for receiving a radiationsource 20, for example, a radioactive source wire. Additionally, theshaft 12 may have a balloon inflation lumen (not shown) to allowinflation of the helical centering balloon 16 from a source proximal tohelical centering balloon 16, as well as a guidewire lumen for receivinga guidewire (not shown), and a support lumen for receiving a supportmandrel (not shown). The balloon inflation lumen, guidewire lumen, andsupport lumen are structures well known by those of ordinary skill inthe art and are not discussed so that the present invention may be moreclearly illustrated. It is to be understood that the present inventioncan be utilized with different guidewire and support systems and thatthe present example is not meant to be limiting on the invention.

The lumen 18 opens at the proximal end of the shaft 12 and terminates atthe distal tip 14. The lumen 18 may be separated from a guidewire lumenby a plug 36. As the helical lobes 26 spiral around the lumen 18, aneffective outer diameter is created which substantially centers thelumen 18 within the lumen of the vessel 32. Upon insertion of aradiation source 20 into the lumen 18, the radiation source 20 is thensubstantially centered within the lumen of the vessel 32 so that anapproximately uniform dose of radiation is delivered to the vessel wall.

In the illustration, it can be seen that the engagement knobs 30 areformed as an integral part of the helical lobes 26, and are positionedalong the exterior portions of the helical lobes 26 to offset thehelical lobes 26 from the walls of the vessel 32. Thus, where prior artcentering catheters utilizing compliant engagement may have had thehelical lobes compliantly engaging the vessel wall, in the presentinvention, the engagement knobs 30 compliantly engage the vessel walland form the auxiliary perfusion channels 34. As the engagement knobs 30may be located on the exterior portions of the helical lobes 26, thespiraling of the helical lobes 26 with the engagement knobs 30 createsan offset that is substantially the same along the length of the helicalcentering balloon 16 such that an effective diameter is maintained andthe radiation source 20 remains substantially centered within the lumenof the vessel 32. In this way, the auxiliary perfusion channels 34provide perfusion in addition to that through the main spiral perfusionchannel 28 to provide an improved perfusion flow rate. Additionally,should the main spiral perfusion channel 28 become partially obstructedor experience a single point failure, the auxiliary perfusion channels34 allow perfusion around the blockage. Thus, the likelihood that an IRTsession will be disrupted due to a low perfusion flow rate may bereduced.

In one embodiment, the proximal end of the helical balloon centeringcatheter 10 may be connected to an afterloader or other device fordelivery of intravascular radiation. In one example, the helical ballooncentering catheter 10 may be connected to an afterloader deviceutilizing a key connector that allows the afterloader device to identifythe particular characteristics of the helical balloon centering catheter10. The afterloader device may then be used to automatically positionthe radiation source 20, i.e., a radioactive source wire, within thehelical balloon centering catheter 10 to deliver the prescribedradiation therapy to the patient. It is to be understood that thehelical balloon centering catheter 10 may be used with hand-loadedradioactive ribbons and wire, or with other radiation delivery devicesand that the use of an afterloader device is not a limitation on thepresent invention.

Radio-opaque markers 22 may be attached to the helical balloon centeringcatheter 10 to delineate a treatment length determined according to aparticular radiotherapy method. The radio-opaque markers 22 may be gold,iridium or other materials commonly used for positioning catheters underfluoroscopy, and are attached by conventional means to the shaft 12. Inone example, the radio-opaque markers 22 may delineate the length withinthe helical centering balloon 16 over which the radiation source 20 willdeliver a radiation dose. Although the present illustration shows asingle radiation source 20 of one length with source end markers 24, itis to be understood that a smaller radiation source may be utilizedaccording to a stepping protocol where the smaller radiation source isadvanced along the lumen 18 until a prescribed dose of radiation isdelivered to the treatment length.

In the present example, the helical centering balloon 16 with theengagement knobs 30 may be fabricated using standard techniques wellknown by those of ordinary skill in the art. In one example, the helicalcentering balloon 16 may be fabricated using a shape mold and materialsof relatively high strength that will expand to a fixed diameter wheninflated, such as relatively high strength polymers, i.e., nylon,polyester, or polyvinyl acetate or polyethylene. The helical centeringballoon 16 may be attached to the shaft 12 by bonds that are located atthe ends, at regular intervals, or are continuous over the length of thehelical centering balloon 16. The bonds may be thermal or ultrasonicwelds, adhesive or solvent bonds, or other conventional means.

FIG. 3A illustrates a transverse sectional view of the embodiment of thepresent invention shown in FIG. 1 taken along line 3—3. In this example,the radiation source 20 within the lumen 18 is substantially centeredwithin the vessel 32 due to the effective diameter 40 created by theprotrusions of the engagement knobs 30 from the helical lobes 26 as thehelical lobes 26 spiral. This allows for a uniform dose of radiation tobe delivered to the vessel wall along the treatment length. In thisexample, the engagement knobs 30 are shown as a hollow, teardrop shapesand form auxiliary perfusion channels 34 to allow additional perfusionpast the helical centering balloon catheter 10. When the helicalcentering balloon 16 is properly inflated, the engagement knobs 30 mayoutwardly protrude a distance 42 of approximately 0.25 mm to 0.75 mm,depending upon the diameter of the helical centering balloon 16. It isto be noted that although the teardrop shape is shown so that theteardrops taper in a direction parallel with the spiral of the helicallobes 26, the teardrop shape may also be perpendicular to the spiral, orat another angle to the spiral. Further, although not shown, as earlierdiscussed, additional lumens for guidewires and/or support wires mayalso be incorporated into the helical centering balloon 16 utilizingstandard techniques well-known by those of ordinary skill in the art. Itis to be understood that although the engagement knobs 30 are formed ashollow protrusions in the present examples, they may be formed by othermethods and in other shapes, so long as the engagement knobs 30 cancompliantly engage the walls of a vessel and allow the formation ofauxiliary channels.

FIG. 3B illustrates a transverse sectional view of the embodiment of thepresent invention shown in FIG. 3A with a blockage 38 of the mainperfusion channel 28. Without the engagement knobs 30, the perfusionflow rate may be negatively impacted by the blockage 38 resulting in adecreased flow rate or single point failure. As earlier described,either of these situations may result in the IRT procedure beingterminated until blood flow is reestablished in the vessel. However, thepresence of the engagement knobs 30, provide the auxiliary channels 34through which perfusion can continue past the blockage 38. This allowsperfusion to reestablish past the blockage 38 in the main perfusionchannel 28, as well as in the auxiliary channels 34. The improvedperfusion may allow the IRT procedure, that may have been terminatedutilizing prior art centering catheters, to continue to completiondespite the blockage 38.

FIG. 4 illustrates another embodiment of the present invention. In thisexample, the helical lobes 26 have engagement knobs 30 that arehemispherical in shape rather than teardrop-shaped as described in thefirst example. In one embodiment, the engagement knobs 30 may be locatedalong the outer spiral midline of the helical lobes 26 with a spacing offive (5) engagement knobs 30 per revolution. Other numbers of engagementknobs 30 and spacing per revolution may also be used, but a spacing ofthree to five (3-5) engagement knobs 30 per revolution is preferred.Further, the engagement knobs 30 may be positioned in patterns, otherthan along the outer spiral midline, for example, in a random pattern,or in multiple rows.

FIG. 5 illustrates a transverse sectional view of the embodiment of thepresent invention shown in FIG. 4 taken along the line 5—5. In thisembodiment, the radiation source 20 within the lumen 18 is substantiallycentered within the vessel 32 due to the effective diameter 40 createdby the protrusions of the engagement knobs 30 from the helical lobes 26as the helical lobes 26 spiral. This allows for a uniform dose ofradiation to be delivered to the vessel wall along the treatment length.In this example, the engagement knobs 30 are shown as a hollow,hemispherical shapes and form auxiliary perfusion channels 34 to allowadditional perfusion past the helical centering balloon catheter 10.When the helical centering balloon 16 is properly inflated, theengagement knobs 30 may outwardly protrude a distance 42 ofapproximately 0.25 mm to 0.75 mm, depending upon the diameter of thehelical centering balloon 16. Further, although not shown, as earlierdiscussed, additional lumens for guidewires and/or support wires mayalso be incorporated into the helical centering balloon 16 utilizingstandard techniques well-known by those of ordinary skill in the art. Itis to be understood that although the engagement knobs 30 are formed ashollow protrusions in the present example, they may be formed by othermethods and in other shapes, so long as the engagement knobs 30 cancompliantly engage the walls of a vessel and allow the formation ofauxiliary channels.

Thus, the present invention includes a centering catheter with improvedperfusion for delivery of intravascular radiation therapy. In oneexample, the present invention provides a helical balloon centeringcatheter with engagement knobs that compliantly engage a vessel wall andform auxiliary perfusion channels. The auxiliary perfusion channelsprovide for perfusion in addition to the perfusion through the mainspiral channel formed between the helical lobes. Additionally, shouldthe main spiral channel become partially obstructed or experience asingle point failure, the auxiliary perfusion channels provide perfusionpaths past the obstruction.

In the foregoing specification, the present invention has been describedwith reference to specific exemplary embodiments thereof. It will,however, be evident that various modifications and changes may be madethereto without departing from the broader spirit and scope of theinvention as set forth in the appended claims. The specification anddrawings are, accordingly, to be regarded in an illustrative rather thana restrictive sense.

I claim:
 1. A catheter for improved perfusion when positioned within avessel, said catheter comprising: a segment having lobes which form atleast one main perfusion channel, said lobes having a plurality ofengagement knobs formed for compliantly engaging the walls of a vesseland forming auxiliary perfusion channels.
 2. The catheter of claim 1wherein said segment is a helical balloon and said lobes are helicallobes.
 3. The catheter of claim 2 wherein said engagement knobs areteardrop-shaped, hollow, protrusions from said helical lobes.
 4. Thecatheter of claim 2 wherein said engagement knobs arehemispherical-shaped, hollow, protrusions from said helical lobes. 5.The catheter of claim 1, wherein each of said auxiliary channels issmaller cross-section relative to said at least one main perfusionchannel.
 6. The catheter of claim 1, wherein said plurality ofengagement knobs center said segment within said vessel.
 7. A catheterfor delivery of intravascular radiation therapy within a vesselcomprising: a flexible, elongate shaft, said shaft having a lumen forreceiving a radiation source; and a segment attached to said shaft, saidsegment comprising helical lobes which form at least one main spiralperfusion channel, said helical lobes having a plurality of engagementknobs outwardly protruding from said helical lobes for compliantlyengaging the walls of said vessel and for forming auxiliary perfusionchannels to allow increased perfusion past said catheter.
 8. Thecatheter of claim 7 wherein said segment is an inflatable, helicalballoon.
 9. The catheter of claim 8 wherein said plurality of engagementknobs are teardrop-shaped, outward, hollow protrusions from said helicallobes.
 10. The catheter of claim 8 wherein said plurality of engagementknobs is hemispherical-shaped, outward, hollow protrusions from saidhelical lobes.
 11. The catheter of claim 7, wherein said plurality ofengagement knobs center said radiation source, within said vessel. 12.The catheter of claim 7, wherein each of said auxiliary channels issmaller cross-section relative to said at least one spiral perfusionchannel.
 13. A catheter for delivery of intravascular radiation therapywithin a vessel, comprising: a flexible, elongate shaft, said shafthaving a proximal end and distal tip, and a central lumen for receivinga radiation source; and an inflatable, helical balloon attached to saidshaft and located proximal to said distal tip, wherein said inflatable,helical balloon comprises helical lobes which form at least one mainspiral perfusion channel, said helical lobes having a plurality ofengagement knobs for compliantly engaging the walls of said vessel andfor forming auxiliary perfusion channels to allow increased perfusion.14. The catheter of claim 13 wherein said plurality of engagement knobsis inflatable, outward, hollow protrusions formed integrally from saidhelical lobes.
 15. The catheter of claim 14 wherein when said helicalballoon is properly inflated said plurality of engagement knobsoutwardly protrude from said helical lobes a distance in the range of0.25 mm to 0.75 mm.
 16. The catheter of claim 14 wherein said pluralityof engagement knobs is teardrop-shaped.
 17. The catheter of claim 16wherein said plurality of engagement knobs are spaced within the rangeof three to five engagement knobs per revolution.
 18. The catheter ofclaim 14 wherein said plurality of engagement knobs ishemispherical-shaped.
 19. The catheter of claim 18 wherein saidplurality of engagement knobs are spaced within the range of three tofive engagement knobs per revolution.
 20. The catheter of claim 13,wherein said plurality of engagement knobs center said radiation source,within said vessel.
 21. The catheter of claim 13, wherein each of saidauxiliary channels is smaller relative to said at least one spiralperfusion channel.
 22. An apparatus, comprising: means for compliantlyengaging a wall of a vessel; and means for forming auxiliary perfusionchannels.
 23. The apparatus of claim 22 wherein said means forcompliantly engaging is a plurality of engagement knobs.
 24. Theapparatus of claim 23 wherein said plurality of engagement knobs isteardrop-shaped.
 25. The apparatus of claim 23 wherein said plurality ofengagement knobs are hemispherical-shaped.
 26. A catheter, comprising: aballoon having a plurality of engagement knobs to engage a vessel wall,wherein each of said plurality of engagement knobs is disposedsubstantially in an axial direction along said balloon with respect toeach other, and wherein said plurality of engagement knobs form aplurality of perfusion channels.
 27. The catheter of claim 26, furthercomprising: a central lumen for receiving a radiation source, whereinsaid plurality of engagement knobs center said radiation source, whenpresent, within said vessel wall, and wherein said plurality ofengagement knobs are disposed substantially in a direction that isperpendicular to said axial direction.
 28. The catheter of claim 26,wherein said balloon comprises a helically-shaped balloon that forms aspiral perfusion channel.
 29. The catheter of claim 26, wherein each ofsaid plurality of engagement knobs is inflatable, outward, hollowprotrusions formed integrally from said balloon, and wherein said axialdirection is an axis between a proximal and distal end of said balloon.